1. Field of the Invention
This invention relates to a reader-printer, and in particular to a reader-printer for sequentially scanning an image on a drum-like photosensitive medium having a curvature in a one-dimensional direction which is rotating or rotationally vibrating by the use of a scanning mirror disposed at the image field side of a projection optical system, thereby causing the image to be projected and formed.
2. Description of the Related Art
In a copying apparatus, a microfilm reader-printer or the like, it has usually been the practice to sequentially scan a light beam from an original passed through a projection optical system by a scanning mirror and project and image the light beam on the surface of a drum-like photosensitive medium.
Image devices using a scanning mirror to direct a light beam passed through a projection optical system onto the surface of a photosensitive medium have heretofore been proposed, for example, in U.S. Pat. No. 4,299,480 and Japanese Laid-Open Patent Application No. 126258/1980.
In the case of a scanning mirror system, as the scanning position of the scanning mirror is farther from a projection lens and accordingly nearer to a screen for the reader, or as the angle of incidence of light with respect to the scanning mirror is greater, the image is more deteriorated and therefore, it is necessary to effect the scanning of the scanning mirror at a position as near as possible to the projection lens and with the angle of incidence being reduced. On the other hand, it is necessary in preventing the deterioration of the image caused by out-of-focus to make the optical distance from a microfilm original to a screen and the optical distance from the original to the photosensitive medium of the printer equal to each other. However, in a scanning mirror system according to the prior art, an attempt to meet the above-described two requirements has led to the increased lengths of the optical path for the reader and the optical path for the printer, which in turn has led to the difficulty in making the reader-printer for microfilm compact.